This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 11-301273, filed Oct. 22, 1999, the entire contents of which are incorporated herein by reference.
The present invention relates to a print head for printing a dot image with drops of ink jet or ejected from ink-jet nozzles, and also relates to a manufacturing method of the print head in which the ink-jet nozzles are formed by laser irradiation.
In a typical ink-jet printer, a print head comprises a head body and an orifice plate attached to an end of the body. The orifice plate includes a plurality of orifices arranged as a raw of ink-jet nozzles. The head body includes a plurality of ink chambers separated by partition walls and an ink-jet actuator of a bubble-jet or Kaiser type, which varies internal pressures of the ink chambers to eject ink. The bubble-jet type ink-jet actuator increases the internal pressure of each ink chamber by generating a bubble at the time of ink ejection. The Kaiser type ink-jet actuator increases the internal pressure of each ink chamber by deforming the partition walls at the time of ink ejection.
The orifice plate is a metal plate in which the plurality of orifices are formed by a plating method generally called electroforming so as to have a forward taper that the orifice diameter gradually decreases in a direction from an ink supply side to an ink discharge side, and which is bonded to the head body with an adhesive. With this plate structure, it is difficult that the orifice pitch is reduced to print a dot image with a higher resolution. Namely, the adhesive flows from the main plate surface into an adjacent orifice during the orifice plate bonding process and easily causes clogging which hinders ink ejection. When the orifice pitch has already been reduced to a value limited by the reason described above, the resolution of a dot image is enhanced using a driving scheme of repeatedly driving the print head while shifting the print head at a pitch narrower than the orifice pitch in a direction that the orifices are arranged. This driving scheme, however, has a drawback that the dot printing position varies due to dependence on the accuracy of a mechanism for shifting the print head, making it difficult to obtain a clear dot image.
Jpn. Pat. Appln. KOKAI Publication No. 5-330064 discloses a technique capable of solving the above-mentioned problem. In this technique, an orifice plate is made of a resin plate previously attached to an end of a head body, and has a plurality of orifices formed by irradiating a laser beam to the resin plate from the ink discharge side. The laser beam is converged by an imaging optical system so that the beam diameter becomes minimum at a focal plane set in a space on the ink discharge side. The laser beam is diverged from the focal plane and reaches the resin plate. In the resin plate, ablation proceeds at portions exposed to the laser beam, to thereby form an orifice of a forward taper that the orifice diameter gradually decreases in a direction from the ink supply side to the ink discharge side.
With this technique, since there is no adhesive flowed into the orifice to cause clogging, the orifice pitch can be sufficiently reduced to print a dot image with a higher resolution. However, if a constant positional relationship between the resin plate and the focal plane of the imaging optical system cannot be maintained for each orifice, the minimum orifice diameter varies due to divergence of the laser beam, making it difficult to print dots of a uniform size.
Further, Jpn. Pat. Appln. KOKAI Publication No. 10-76666 discloses an orifice formation technique capable of reducing the irregularity in the minimum orifice diameter. In this technique, a plurality of orifices are formed by irradiating laser beams from the ink supply side and the ink discharge side to a resin plate. The laser beam from the ink supply side is converged by an imaging optical system so that the beam diameter becomes minimum at a focal plane set in a space on the ink discharge side. The laser beam reaches the resin plate on the way to the focal plane. In the resin plate, ablation proceeds at portions exposed to the laser beam, to thereby form an orifice of a forward taper that the orifice diameter gradually decreases in a direction from the ink supply side to the ink discharge side. The laser beam from the ink discharge side is converged by the imaging optical system so that the beam diameter becomes minimum at a focal plane set at a space on the ink supply side. The laser beam reaches the resin plate on the way to the focal plane. In the resin plate, ablation proceeds at portions exposed to the laser beam, to thereby shape the orifice into a reverse taper near the resin plate surface located on the ink discharge side. This structure compensates for variations in the orifice diameters on the ink discharge side. However, the orifice formation technique requires the laser beam irradiated from the ink supply side onto the resin plate to form each orifice, it is difficult that the resin plate is previously attached to the head body end without adversely affecting the laser beam irradiation. If the resin plate is bonded to the head body with an adhesive after the orifice formation, there is a possibility that, as mentioned above, the adhesive flows from a main plate surface into an adjacent orifice and clogs it. Accordingly, the orifice pitch cannot be sufficiently reduced to print a high-resolution dot image. Since the laser beams are irradiated to the resin plate from the ink discharge side and from the ink supply side, displacement of the boundary between the forward taper and the reverse taper easily occurs in each orifice due to an alignment error of the laser beams. This displacement causes turbulence in a flow of ink which is supplied to the orifice for ejection by changing the internal pressure of the ink chamber. As a result, each ink drop is not ejected in a uniform direction.
An object of the present invention is to provide a print head and a manufacturing method thereof for improving a print resolution without degrading print quality.
According to the present invention, there is provided a print head which comprises an orifice plate having a plurality of orifices arranged as ink-jet nozzles; and a head body partitioned into a plurality of ink chambers and integrated with the orifice plate such that ink is guided from the ink chambers to the orifices, for increasing an internal pressure of each ink chamber to eject ink from a corresponding orifice, wherein each orifice has a constriction for restricting an ink-jet error angle to a range of xc2x15 mrad with respect to a center axis thereof.
According to the present invention, there is provided a print head manufacturing method which comprises a bonding step of bonding an orifice plate to a head body partitioned into a plurality of ink chambers by an adhesive, a perforation step of forming a plurality of orifices in the orifice plate by irradiating a laser beam such that the orifices are arranged as ink-jet nozzles communicated with the ink chambers to eject ink upon increase in the internal pressures of the ink chambers, wherein the perforation step includes a shaping step of shaping each orifice by converging the laser beam using an imaging optical system whose focal plane is set inside the orifice plate so as to simultaneously form in the orifice a forward taper whose aperture size gradually decreases to a predetermined value in a thickness direction of the orifice plate from an ink supply side to an ink discharge side, and a non-forward taper communicated with the forward taper.
In the print head described above, the constriction of each orifice restricts the ink-jet error angle to a range of xc2x15 mrad with respect to a center axis of the orifice. Therefore, positional deviation is reduced to 1 xcexcm or less in a plane distanced by 1 mm from the orifice. Thus, the print quality is not degraded even when the print resolution is improved.
Further, in the print head manufacturing method described above, the shaping step shapes each orifice by converging the laser beam using an imaging optical system whose focal plane is set inside the orifice plate so as to simultaneously form in the orifice a forward taper whose aperture size gradually decreases to a predetermined value in a thickness direction of the orifice plate from an ink supply side to an ink discharge side, and a non-forward taper communicated with the forward taper. That is, it is not necessary to irradiate laser beams from the both sides of the orifice plate. Accordingly, even if the bonding step is performed prior to the perforation step, each orifice can be formed in the perforation step by irradiating a laser beam to that surface of the orifice which is located on the ink discharge side. Since the orifice is formed after the bonding step, it is possible to prevent clogging caused by an adhesive flowed into the orifice. Further, the constriction of each orifice sufficiently reduces an ink-jet error angle with respect to the center axis of the orifice, so that the print resolution can be improved without degrading the print quality.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.